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A8502 View Datasheet(PDF) - Allegro MicroSystems

Part Name
Description
MFG CO.
'A8502' PDF : 35 Pages View PDF
A8502
Wide Input Voltage Range, High Efficiency
Fault Tolerant LED Driver
Boost switch overcurrent protection
The boost switch is protected with cycle-by-cycle current limiting
set at a minimum of 3.0 A. There is also a secondary current limit
that is sensed on the boost switch. When detected this current
limit immediately shuts down the A8502. The level of this cur-
rent limit is set above the cycle-by-cycle current limit to protect
the switch from destructive currents when the boost inductor is
shorted. Various boost switch overcurrent conditions are shown in
figures 25 through 27.
SW node
C1
SW node
C2
IL
VOUT
PWM/EN
C3
C4
t
Figure 25. Normal operation of the switch node (SW); inductor current
(IL) and output voltage (VOUT) for 9 series LEDs in each of 2 strings
configuration; shows SW node (ch1, 20 V/div.), inductor current, IL
(ch2, 1 A/div.), VOUT (ch3, 10 V/div.), and PWM/EN (ch4, 5 V/div.),
time = 2 μs/div.
C1
IL
VOUT
C2
PWM/EN
C3
C4
t
Figure 26. Cycle-by-cycle current limiting; inductor current (yellow trace, IL),
note reduction in output voltage as compared to normal operation with the
same configuration (figure 23); shows SW node (ch1, 20 V/div.), inductor
current, IL (ch2, 1 A/div.), VOUT (ch3, 10 V/div.), and PWM/EN (ch4,
5 V/div.), time = 2 μs/div.
PWM/EN
C1
FAULT
C2
SW node
C3
IL
C4
t
Figure 27. Secondary boost switch current limit; when this limit is hit, the
A8502 immediately shuts down; shows PWM/EN (ch1, 5 V/div.), ¯F¯¯A¯U¯¯L¯¯T¯
(ch2, 5 V/div.), SW node (ch3, 50 V/div.), and inductor current, IL (ch4,
2 A/div.), time = 100 ns/div.
Allegro MicroSystems, Inc.
21
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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